The present invention relates generally to the field of the high pressure fittings and specifically to fittings that supply ultra clean high pressure gas for use in semiconductor processing.
High pressure processing of semiconductor devices provides improved filling of vias and other high aspect ratio surface features. However the equipment costs associated with machining and assembling the fittings that deliver high pressure fluid (e.g., high pressure gases) to a processing chamber, and the down time associated with fitting repair, reduces the desirability of high pressure processing.
In order to understand the significance of the present invention, it is first necessary to understand conventional high pressure fitting designs. FIG. 1 shows a side elevational view representative of a conventional high pressure fitting 11, a high pressure tube 13 and a coupling assembly 15 for coupling the high pressure tube 13 to the high pressure fitting 11. Within FIG. 1 all parts are shown in section to facilitate explanation of their interior surface features.
The high pressure fitting 11 comprises a fluid passageway 17 having an abrupt direction change (i.e., a corner 19) having an inner edge 21a and an outer edge 21b; and a cavity having a threaded interior surface (i.e., threaded cavity 23). The fluid passageway 17 has a chamfered region 25 that connects the threaded cavity 23. Similarly the high pressure tube 13 has a coned end 27 with a chamfer that corresponds to the chamfer of the fluid passageway 17's chamfered region 25. A fluid tight seal is formed between the high pressure fitting 11 and the high pressure tube 13 which (because they are both metal parts such as stainless steel) exhibit metal to metal deformation when forced against each other as described below. The high pressure tube 13 further comprises a threaded region 29 for mating with the coupling assembly 15.
The coupling assembly 15 comprises a nut 31 and a collar 32. The interior surface (not shown) of the collar 32 is threaded so as to threadingly engage the threaded region 29 of the high pressure tube 13.
The nut 31 has openings at both of its ends and a continuous passageway therebetween such that the nut 31 may be slidably mounted on the high pressure tube 13. The nut 31 has an interior surface profile that comprises a first interior region 33 having an interior diameter sized to receive the collar 32 with minimum clearance, and a second interior region 35 having an interior diameter sized to receive the high pressure tube 13 with a small clearance. A sloped region 37 on the interior of the nut 31, which matingly corresponds to a chamfer 39 on the collar 32, transitions between the first and second interior regions 33, 35. The exterior surface of the nut 31 comprises an exterior threaded region 40 and a sextagonal head region 41.
In operation, to assemble a flow system the nut 31 is slid over the high pressure tube 13 and the collar 32 is then threaded on the threaded region 29 of the high pressure tube 13, and the nut 31 is slid toward the collar 32 until the collar 32 is completely recessed within the first interior region 33 of the nut 31. The exterior threaded region 40 of the nut 31 is then screwed into the threaded cavity 23 of the high pressure fitting 11. Because the interior region 33 of the nut 31 presses against the collar 32, the collar 32, which is threadingly coupled to the high pressure tube 13, forces the coned end 27 of the high pressure tube 13 against the chamfered region 25 of the high pressure fitting 11, forming a fluid tight seal therebetween.
Sufficient threaded engagement must exist between the exterior threaded region 40 and the threaded cavity 23 of the high pressure fitting 11 to withstand the forces applied thereto by the high pressure flow which is transmitted therethrough. If the collar 32 is threaded onto the high pressure tube 13 too far from the chamfered end 27 (e.g., too far in the direction of the arrow "A" of FIG. 1) the nut 31 will not be able to move far enough toward the high pressure fitting 11 (e.g., far enough in the direction of the arrow "B" of FIG. 1) to achieve sufficient threaded engagement therebetween. Additionally the angle of the chamfered end 27, which may vary from tube to tube, controls the depth with which the high pressure tube 13 extends into the fluid passageway 17 of the high pressure fitting 11, and thus controls the overall length of the assembled high pressure fitting 11 and the high pressure tube 13 (i.e., the fitting/tube assembly).
In order to form a flow system the assembly process described above is repeated. That is, another coupling assembly 15 may be slid onto another high pressure tube 13, assembled, and screwed into an additional threaded cavity (not shown) within the high pressure fitting 11, and/or an additional collar 32 can be screwed onto a second chamfered end (not shown) of the high pressure tube 13, and an additional coupling assembly assembled and screwed into an additional high pressure fitting, etc.
As discernible from the above description, due to the many interlocking parts and the numerous chamfered and/or threaded surfaces, conventional high pressure fittings are complex and costly to manufacture and assemble. Moreover, conventional high pressure fittings are inherently subject to particle generation. For example, within a corner, particles of the inner edge 21a may wear off during high pressure operation. Particles also may be generated when screwing one surface to another, or when pressing metal surfaces against one another (e.g., the coned end 27 of the high pressure tube 13 against the chamfered region 25 of the high pressure fitting 11) to achieve metal to metal deformation. Further, after repeated uses the metal surfaces of the high pressure tube 13 and the chamfered region 25 of the high pressure fitting 11 are unable to deform an amount sufficient to form a fluid tight seal. Conventional fittings and tubes therefore must be frequently replaced.
Perhaps the most troublesome feature of these conventional fittings is the difficulty associated with fitting replacement and the difficulty associated with forming a flow system which is compact and symmetrical. Due to the high cost of clean rooms, and the need to access processing chambers without obstruction, a flow system's overall size and symmetry are important. With conventional high pressure fittings, the variable length of each fitting/tube assembly renders building a symmetrical flow system nearly impossible, and removal of a single coupling assembly 15 from a high pressure fitting 11 extremely difficult and time consuming. To remove a coupling assembly 15 from a high pressure fitting 11 the coupling assembly 15 must be unscrewed and the high pressure tube 13 withdrawn from the threaded region 23 of the high pressure fitting 11, which, if achieved, will move not only the relevant coupling assembly 15 away from the high pressure fitting 11 but also will move the entire high pressure tube 13 and any other high pressure fittings 11 coupled thereto. Accordingly, once assembled a conventional high pressure flow system experiences virtual grid lock; reconfiguration or repair of a single fitting/tube joint is impossible without adjustment of numerous surrounding fitting/tube joints.
Accordingly a need exists for a new high pressure fitting which facilitates assembly and repair while being inexpensively manufacturable and less likely to generate particles.